This application is based on and incorporates herein by reference Japanese Patent Applications No. 2002-171416 filed on Jun. 12, 2002 and No. 2002-260443 filed on Sep. 5, 2002.
The present invention relates to a failure detecting device and method for detecting a failure of an intake system of internal combustion engines in, for example, vehicles and so on.
Air cleaner is provided in an intake passage of an internal combustion engine to eliminate foreign matters, such as dust, or the like, contained in air. When foreign matters, such as dust, or the like, accumulate in the air cleaner, they become intake resistance when air is introduced into the internal combustion engine.
Conventionally, JP-3055357 discloses a device for detecting a failure of an intake system. In this technology, a throttle valve is adjusted to afford a predetermined quantity of air. Accordingly, an opening position of the throttle valve is controlled at all times to afford a predetermined quantity of air as required. In such a control of the throttle valve, clogging of an air cleaner is detected by the comparison of an actual throttle opening position when a quantity of air sucked by an internal combustion engine becomes a predetermined quantity and a preset throttle opening position. The preset throttle opening position is an opening position of the throttle valve, by which the predetermined air quantity is attained in a state, in which foreign matters, such as dust, or the like, are not entrained in the air cleaner.
That is, since an increase in intake resistance is caused when foreign matters, such as dust, or the like, accumulate in the air cleaner, an opening position of the throttle valve is controlled to become larger in order to afford the predetermined air quantity. Hereupon, clogging of the air cleaner is detected by the comparison of an actual throttle opening position and a preset throttle opening position.
Since the above device detects clogging when the predetermined air quantity is afforded, however, there is a possibility that in the case where foreign matters are increased in accumulation to increase the intake resistance, the predetermined air quantity cannot be afforded and the detection of clogging cannot be performed even when the throttle valve is regulated.
The internal combustion engine is supplied with fuel by a fuel injection system. One type of fuel injection control system is referred to as a D-J system for detecting, as a parameter of an intake air sucking state, an intake pressure downstream of the throttle valve to determine a fundamental fuel injection quantity in accordance with the intake pressure and an engine speed. The other type of fuel injection control system is referred to as an L-J system for detecting, as a parameter of the intake air sucking state, the intake air quantity upstream of the throttle valve to determine the fundamental fuel injection quantity in accordance with the intake air quantity and an engine speed.
Hereupon, when gas-tightness of the intake system is damaged (a leakage abnormality) due to disengagement and fracture of pipes, such as an intake manifold, or the like, downstream of the throttle valve, air flows into the intake system from a location, in which leakage abnormality is present, because of a negative pressure downstream of the throttle valve, so that the air quantity taken into a cylinder becomes larger than the air quantity passing through the throttle valve.
In the internal combustion engine of the D-J system, the intake pressure rises relative to that in a normal state since air flows into the intake system from a location, in which leakage abnormality is present. Correspondingly, the fuel injection quantity becomes excessively larger than required, and the engine speed is excessively increased. Thus, deceleration becomes hard, and an idling speed is increased, thereby incurring a worse fuel consumption and an increase in exhaust gases.
Also, in the internal combustion engine of the L-J system, corresponding to air in flowing from a location, in which leakage abnormality is present, the intake air quantity actually taken into the cylinder becomes excessive relative to the detected intake quantity. Thus it gets into an over-lean fuel condition, which will incur engine stall, bad drivability, and degradation in cleanliness of exhaust gases.
Therefore, there is a need of taking fail-safe measures to detect leakage abnormality in the intake system and to warn a driver.
For example, in the D-J system disclosed in JP 2518317, an upper limit intake pressure is set according to a throttle opening position. When the detected intake pressure exceeds the upper limit intake pressure, it is determined that leakage abnormality is present downstream the throttle valve in an intake system. The rotation speed of the internal combustion engine above which fuel injection is inhibited (fuel cut-off) as fail-safe measures is lowered.
Also, in the D-J system disclosed in JP-B2-3-16498, the intake pressure is assumed according to the throttle opening position and the engine speed. When the detected intake pressure exceeds the assumed intake pressure, the fuel injection quantity is fixed to a predetermined value.
Also, in the L-J system disclosed in JP-A-5-280403, the basic injection quantity is estimated on the basis of the throttle opening position and the engine speed. In the case where the actual injection quantity is smaller than the basic injection quantity and correction of a fuel injection quantity performed by air-fuel ratio causes an increase in the injection quantity, it is determined that leakage abnormality is present in the intake system.
In the above conventional systems, sensors for detecting the intake pressure and the intake air quantity are used. However, in the case where owing to variation in characteristics, such sensors generate errors in output detection values relative to actual values, it is likely to determine the intake system, in which leakage abnormality is present, to be normal.
In JP 2901612, in a transient state, such as an engine start or the like, the threshold value for determining whether a leakage abnormality is present is corrected in a manner to enlarge a tolerance, which is determined to be normal, thereby avoiding an erroneous determination. In the case where abnormality is actually present, however, it is likely to fail to detect it. Thus, such measures are not necessarily adequate.
The present invention has its first object to provide an intake system failure detecting device and method capable of surely detecting clogging of air cleaner even in the case where foreign matters are increased in accumulation to increase an intake resistance.
The present invention has its second object to provide an intake system failure detecting device and method capable of detecting leakage abnormality in an intake system.
For attaining the first object, according to the present invention, an actual load of an internal combustion engine and an opening position of a throttle valve are detected. A reference load of the internal combustion engine is predetermined for each opening position of the throttle valve. Whether a failure is present in the intake system is determined based on the detected actual load and the predetermined reference load for each opening position of the throttle valve.
For attaining the second object, according to the second invention, leakage abnormality of an intake system downstream a throttle valve is determined by making a comparison between a detection value of an intake air sucking state and a reference value of an intake air sucking state at the time of normality free from the leakage abnormality. The reference value is set in correspondence with a load on the internal combustion engine. The leakage abnormality is determined when the difference between the detection value and the reference value in each of a plurality of loads different in magnitude becomes larger as the load becomes lower.